Reformer reactor and method for converting hydrocarbon fuels into hydrogen rich gas

ABSTRACT

A reformer reactor is provided for converting hydrocarbon fuel into hydrogen rich gas by auto-thermal reaction process having a cylindrically shaped and double walled, housing with two side faces forming a. reaction chamber of the reformer. Additionally, a fuel inlet is provided in one of the to side faces for providing hydrocarbon fuels into the reaction chamber, wherein further a fuel preheating means is provided which preheats the hydrocarbon fuel before the hydrocarbon fuel enters the reaction chamber.

BACKGROUND AND SUMMARY

The present application is a divisional of U.S. application Ser. No.13/002,338 filed Jan. 3, 2011, which was the U.S. national stage ofInternational App. PCT/SE2008/000422 filed Jul. 2, 2008, both of whichare incorporated by reference.

The present invention relates to a reformer reactor for convertinghydrocarbon fuels into hydrogen rich gas for fuel cells and/or exhausttreatment applications by auto-thermal reaction and a method forconverting hydrocarbon fuels into hydrogen rich gas using the reformerreactor.

In the state of the art it is well known to produce hydrogen rich gasfor the use in fuels cells of transportation devices by reforminghydrocarbon fuels, like gasoline or diesel fuels. Conventionally,hydrogen is produced in large-scale industrial facilities and thenstored on board of the transportation devices. The recent development ofsmall-scale on-board hydrogen sources, so-called reformer reactors,provides a possibility for producing hydrogen on demand without thenecessity of hydrogen storage.

In general there are three known methods of reforming gaseous or liquidhydrocarbon fuels into hydrogen: catalytic steam reforming, partialoxidation reforming and auto-thermal reforming.

In catalytic steam reforming processes a mixture of steam andhydrocarbon fuel is exposed to a suitable catalyst, like nickel, at ahigh temperature (between 7000 C and 1000 C). The reaction is highlyendothermic. and requires an external source of heat and a source ofsteam.

In partial oxidation reforming processes a mixture of hydrogen fuel andan oxygen containing gas, like ambient air, are fed as feed gas into areaction chamber, preferably in the presence of a catalyst. The catalystused is normally made from a noble metal or nickel and the temperatureis between 700° C. and 1700° C. The reaction is highly exothermic andonce started generates sufficient heat to be self sustaining. In orderto promote the oxidation reaction, it is necessary to reduce temperaturevariations n the reactor.

Auto-thermal reforming processes are a combination of steam reformingand partial oxidation reforming. Waste heat from the partial oxidationreforming reaction is used to heat the endothermic steam reformingreaction.

The natural by-products of all reforming processes are carbon monoxideand carbon dioxides. But, since the hydrocarbon fuels were not designedas a feed stock for generating hydrogen, there are also otherby-products such as sulphur. These byproducts may be harmful to the fuelcells and should therefore be removed by subsequent steps outside thereformer reactor. Additionally, hydrocarbon fuels, especially diesel,can in the catalyst produce soot as a byproduct if the mixing in thereactor is poor. Soot particles again, are very harmful to the fuelcells and care must be taken to avoid the formation of soot in thereformer.

From the state of the art, patent application U.S. Pat. No. 6,770,106, apartial oxidizing, reformer for reforming feed gas containinghydrocarbon or methane, oxygen and water, is known, wherein thereduction of temperature variations is achieved by an reactor beingcovered with a passage for feed gas, which is heated by the reactionheat in the reactor and therefore thermally isolate the reactor.Thereby, temperature variations inside the reactor can be reduced. Forheating the feed gas, the reaction beat can be recovered by a heatexchanger.

Additionally, it has been found that a successful and efficientconversion of the feed gas into a hydrogen gas is dependent on asuccessful mixing of the reactants, namely hydrocarbon fuel and anoxidizing agent. The disadvantage of the known state of the art is that,since the mixing of the reactants is performed in a further, externallyarranged mixer, a perfect atomization or vaporization of the hydrocarbonfuel and the oxidants without condensation of the fuel in the reactionchamber of the reformer cannot be provided.

For solving this problem it has been proposed in the state of the arte.g. to mix fuel and oxidizing agent in the reformer and, preferably,even to vaporize injected fuel by preheating the incoming air stream tobe mixed with the fuel, or by preheating a reformer surface forreceiving a fuel spray. Since none of the prior art approaches isentirely successful in providing a reliable, complete vaporization ofthe injected hydrocarbon fuel, it has been proposed in the EuropeanPatent Application EP 1 927 579, to provide a metallic element insidethe reaction chamber of the reactor to provide a high temperature, highsurface area for fuel vaporization.

Such a. known fuel vaporizer can be e.g. an electrically-conductivemetallic material in the form of a foam or spunwoven fibres onto whichthe fuel is sprayed, or even in the form of a cylindrical elementlongitudinally arranged along the inside walls of the reactor.

This known reformer has the disadvantage that the material from whichthe vaporizer is formed must be carefully selected. On the one hand itmust have a moderate Ohmic resistance so that the vaporizer can beheated very quickly to the desired temperature, but, on the other hand,it must be chemically inert to the operating environments of thereactor. The material requirements to the cylindrically shaped vaporizerare less demanding, but this vaporizer has the disadvantage, that theheating load is increased as the vaporizer is fully exposed to bothincoming air and fuel air mixture which both are also acting as coolant.

Therefore, it is desirable to provide a reformer reactor and as methodfor convening hydrocarbon fuels into hydrogen rich gas which provides aneasy and material independent atomization of the hydrocarbon fuel intothe oxidant.

According to an aspect of the present invention a substantially perfectfuel atomization and subsequent gas mixture can be achieved bypre-heating the hydrocarbon fuel before introducing and mixing thehydrocarbon fuel with an oxidizing agent. Such as preheating can beachieved by preheating means which is arranged outside of the reactionchamber of the reformer, Preferably, the preheating means is a separatedevice being arranged upstream to a fuel inlet, but it is also possibleto integrate the fuel inlet and the preheating means in a single device.Particularly in the preferred case, where a fuel injector is used asfuel inlet, it is advantageous to heat the injector, whereby the fuel ispreheated. Thereby, it is further preferred if the fuel inlet is in heatconductive contact with a side wall of the reaction chamber, so thatheat generated in the reaction chamber can be transferred to theinjector for preheating the fuel.

In a further preferred embodiment, the temperature of the preheated fuelis adapted to be close to, but below the lowest boiling point of thefuel, whereby the preferred heat required for substantially perfectatomization or vaporization is provided.

According to a further advantageous embodiment, also the oxidizing agentis preheated prior to mixing with the hydrocarbon fuel, preferably to astemperature in the same range or higher than the temperature of thepreheated fuel. This substantially prevents unwanted condensation of thefuel or the oxidizing agent, which could result in a shortened life timeof the reformer. The preheating of the oxidizing agent can be preferablyperformed by using a reformer reactor having an inner wall and an outerwall forming a space in-between, wherein said space is designed asoxidizing agent passage between an oxidizing agent supply port providedin the outer wall and an oxidizing agent inlet provided in the innerwall. The inner wall is heated by the heat of the reaction taking placeinside the reaction chamber, whereby in turn the oxidizing agent ispreheated by the inner wall by heat transfer from the inner wall to theoxidizing agent.

The combination of fuel preheating and mixing the atomized fuel with theoxidizing agent results in a substantially completely homogenousreactant mixture and preheating of the oxidizing agent preventscondensation. The thereby achieved substantially homogenous mixtureallows for a substantially complete conversion of the hydrocarbon fuelwhich in turn allows for an efficient production of fuel cell gradehydrogen from heavy hydrocarbon fuel.

An advantageous side effect of the above described preheating of theoxidizing agent by heat transfer from the inner wall of the reformer tothe oxidizing, agent is that the heat transfer also cools the inner wallto a temperature, at which the formation of soot by burning of fuelparticles coming in contact with the inner walls is substantiallyprevented.

Generally, there is the possibility to provide the reactor with anexternal cooling device but this increases the dimension of the reactorand adds a further consumer of energy to the system being supplied withenergy by the fuel cells. Therefore, the preferred embodiment uses therelatively cool oxidizing agent for cooling the inner wall of thereactor. That means at the same time that a thermal isolation of theinner wall can be left out, whereby the dimension of the reactor isfurther reduced.

Another advantage of the cooling of the inner wall is that thetemperature inside the reaction chamber can be held constant and thetemperature of the oxidizing agent can be controlled.

As shown in another preferred embodiment of the present invention, theoxidizing agent inlet provided in the inner wall of the housing isformed as a plurality of orifices, particularly holes or minute slits.This facilitates the substantially homogenous distribution of oxidizingagent in the reaction chamber, Preferably, size, shape and/or locationof the orifices can vary according to the used oxidizing agent. the usedhydrocarbon fuel and/or their temperature. Most preferably, theoxidizing agent inlet is provided in the vicinity of the fuel inlet.

Another preferred embodiment is provided with a catalyst for theauto-thermal reaction inside the reaction chamber to accelerate theconversion of hydrocarbon fuel into hydrogen rich gas. Since thepremixing is performed in the inventive manner a substantiallycompletely homogenous mixture can be placed in contact with the catalystand the substantial prevention of condensation also substantiallyprevents deactivation of the catalyst and thereby prolongs the life-timeof the reformer. Preferably, the catalyst can be a ceramic monolith ormetal grid. Preferably, the size of the orifices and the distancebetween the orifices and the fuel inlet are designed so that an optimalturbulent mixture is achieved and so that the oxidizing, agent/fuelmixture is substantially completely homogenous before coming in contactwith the catalyst. The distance between the mixing zone (orificelocation) and the catalyst is also constructed so that the oxidizingagent achieves a mixture stabilization without causing auto oxidation ofthe oxidizing, agent/fuel mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, a preferred embodiment of the reformer reactoraccording to the invention will be discussed with help of a drawing. Thedescription is considered as exemplification of the principles of theinvention and is not intended to limit the scope of the claims.

FIG. 1 shows a schematic view of a preferred embodiment of said reformerreactor according to the invention,

BACKGROUND AND SUMMARY

The reformer reactor 1 in FIG. 1 comprises a housing 2 with an innerwall 4, an outer wall 6 and side walls 8 a, 8 b. Inner wail 4 and sidewalls 8 a, 8 b define a reaction chamber 10 in which hydrocarbon fuel 20and oxidizing agent 14 are brought together and an auto-thermal reactioncan take place.

Inner wall 4 and outer wall 6 define a space 12 between them. The space12 in turn forms a passage for oxidizing agent 14 between an oxidizingagent supply port 16 and an oxidizing agent inlet 18.

Additionally, reformer reactor 1 includes a catalyst 28 for catalyzingthe auto-thermal reaction in reaction chamber 10. The catalyst 28accelerates the auto-thermal reaction, but it is also possible to use areformer reactor according to the present invention without a catalyst.The catalyst 28 is preferably a metal grid or ceramic monolith, but itis possible to use any other suitable substrate for the design ofcatalyst 28.

The oxidizing agent inlet 18 is formed as a plurality of orifices,particularly as holes and/or minute slits, the size, shape and locationof which vary depending on the used oxidizing agent 14, the usedhydrocarbon fuel 20 and their temperature. The plurality of orifices canhave uniform size and shape, but it is also possible that the orificesvary in size and shape among each other. Preferably, the size of theorifices and the distance between the orifices and the fuel inlet aredesigned so that an optimal turbulent mixture is achieved and so thatthe oxidizing agent/fuel mixture is substantially completely homogenousbefore coming in contact with the catalyst 28. The distance D betweenthe mixing zone (location of the orifices 18) and the catalyst 28 isalso constructed so that the oxidizing agent achieves a mixturestabilization without causing auto oxidation of the oxidizing agent/fuelmixture.

Further, reformer reactor 1 has a hydrocarbon fuel inlet 22 which islocated in side wall 8 a of housing 2. Preferably, the fuel inlet 22 isformed as a fuel injector which provides a fuel spray in reactionchamber 10. A reformer gas outlet 24 is provided in the opposite sidewall 8 b of housing 2. Reformer gas 26 is a hydrogen rich gas which canbe used for operating of fuel cells and is the product of theauto-thermal reaction.

As shown in FIG. 1, the reformer reactor 1 further comprises apreheating means 30 for preheating the hydrocarbon fuel 20. In FIG. 1,the fuel preheating means is illustrated as separate device 30, but itis also possible to integrate fuel injector 22 and fuel preheating means30 into a single device. If the fuel injector .22 is additionally inheat conductive contact with the side wall 8 a, heat generated in thereaction chamber 10 can be transferred to the fuel injector 22, where itcan be used to preheat the hydrocarbon fuel 20.

In the following the operation of the reformer reactor 1 is described bymeans of the exemplary conversion of diesel as hydrocarbon fuel intohydrogen with an air/steam-mixture as oxidizing, agent. The reaction furthe con version is auto-thermal.

According to the invention air and steam are mixed before theair/steam-mixture 14 is injected by oxidizing agent supply port 16 intospace 12 which serves as air/steam passage for transportation of theair/steam mixture 14 from oxidizing agent supply port 16 to oxidizingagent inlet 18 of the reformer reactor 1.

On the way to the plurality of inlet orifices 18 in the inner wall 4 ofhousing 2 the air/steam-mixture 14 is preheated by heat transfer fromthe inner wall into the air/steam mixture, whereby the heat transferalso cools the inner wall 4 of reaction chamber 10. B cooling the innerwall 4 of the reaction chamber 10 the risk of diesel fuel molecules inthe reaction chamber 10 burning to soot when hitting the reactionchamber wall, is reduced. The inner wall 4 of the reaction chamber 10 isheated by the substantially homogenous oxidation taking place in thereaction chamber 10 when oxygen coming from the air/steam-mixture 14reacts with “lighter” hydrocarbon molecules of the diesel fuel 20 havingshorter chains (CxHy+O2->CO2+CO+H2O).

The air/steam-mixture 14 is forced through the orifices 18 into thereaction chamber 10 of the reactor forming a substantially homogenousair/steam fume in the reaction chamber 10, where it is mixed with dieselfuel 20 being sprayed into the airs team fume by means of fuel injector22.

For a successful mixing of the diesel fuel 20 and air/steam fume 14 asubstantially perfect atomization or vaporization of the diesel fuel 20into the air/steam fume 14 is required in order to substantially preventcondensation of the fuel 20 or air/steam fume 14. Since such an unwantedcondensation likely occurs due to temperature differences between thepreheated air/steam fume 14 and the normally cooler diesel fuel 20,according to the invention, also the diesel fuel 20 is preheated bypreheating means 30. A substantially perfect fuel atomization orvaporization and subsequent air/steam mixture is achieved by preheatingthe diesel fuel 20 to a temperature close to, but below the lowestboiling point of the fuel, whereby also heat for a substantially perfectatomization or vaporization is provided. Preferably, also the air/steamfume 14 is preheated to a temperature in the same range or higher thanthe temperature of the diesel fuel 20, whereby an elevated temperaturebetween fuel 20 and steam 14 is provided, which in turn substantiallyprevents condensation.

Since fuel, and particularly diesel fuel, is a mixture of differentcomponents, whereby each of which has a different boiling point, theair/steam mixture is preferably preheated to a temperature higher thanthe boiling point of the lightest components of the diesel fuel whichdefines the lowest boiling point of the diesel fuel. If the temperatureof the preheated air/steam mixture is higher than the temperature givenby the lowest boiling point of the diesel fuel, the light components ofthe fuel are substantially prevented from condensation and thetemperature of the fuel/air/steam mixture converges to the boilingpoints of the heavier components of the fuel, whereby the substantiallycomplete vaporization of the fuel can be easier achieved. It should benoted that a condensation of the air/steam mixture due to coming intocontact with the “cooler” preheated fuel does not take place. since theair/steam mixtures is not cooled below its boiling point when it coniesin contact with the preheated fuel.

The combination of fuel preheating and mixing the atomized fuel with theair/steam fume results in a substantially completely homogenous reactantmixture that allows for substantially complete conversion of thehydrocarbon fuel which in turn allows for an efficient production offuel cell grade hydrogen.

Dependent on the location, size, and distance between the orifices andthe fuel injector 22, inside reaction chamber 10 a turbulent mixture ofthe air/steam-fume with the diesel fuel spray is achieved, so that themixture is substantially completely homogenous before it comes intocontact with the catalyst 28.

This substantially homogeneous gas mixture is then introduced intocatalyst 28 were the hydrocarbons of the diesel fuel 20 are undergoingthe auto-thermal reaction process. In the auto-thermal reaction processtaking place inside the catalyst hydrogen (H), CO and CO2 are producedas dominant process products. These products are processed in subsequentsteps outside the reformer with the aim to separate H from all otherprocess products.

REFERENCE LIST

-   1 Reformer reactor-   2 housing-   4 inner wall-   6 outer wall-   8 a, b> sides faces-   10 reaction chamber-   12 space=oxidizing agent passage-   14 oxidizing agent-   16 oxidizing agent supply port-   18 oxidizing agent inlet-   20 hydrocarbon fuel-   22 hydrocarbon fuel inlet-   24 hydrogen rich gas outlet-   26 hydrogen rich gas-   28 catalyst-   30 preheating means

1-13. (canceled)
 14. A method for converting hydrocarbon fuels into ahydrogen rich gas for fuel cells and/or exhaust gas treatmentapplications by auto-them al reaction using a reformer reactor having ahousing with two side faces forming a reaction chamber of the reformerreactor, a fuel inlet which is provided in one of the two side faces forproviding hydrocarbon fuels into the reaction chamber and an oxidizingagent inlet for providing an oxidizing agent into the reaction chamber,comprising: preheating the oxidizing agent to a temperaturesubstantially at or above the boiling point of the hydrocarbon fuel;preheating the hydrocarbon fuel to a temperature substantially below itsboiling point prior to introduction into the reaction chamber; andintroducing the hydrocarbon fuel and the oxidizing agent into thereaction chamber
 15. A method according, to claim 14, comprisingpreheating the hydrocarbon fuel and the oxidizing agent prior to theirintroduction into the reaction chamber.
 16. A method according to claim14, wherein air and steam are used as oxidizing agent, and wherein theair and steam are premixed before the air and steam mixture ispreheated.
 17. A method according to claim 14, wherein the hydrocarbonfuel is a mixture of different components, and wherein at least one ofthe oxidizing agent is preheated to a temperature higher than a boilingpoint of a lightest component of the hydrocarbon fuel, and thehydrocarbon fuel is preheated to a temperature below the boiling pointof the lightest component of the hydrocarbon fuel.
 18. A methodaccording to claim 14, further comprising at least one of mixing thehydrocarbon fuel and the oxidizing agent in the reaction chamber to aoxidizing homogenous mixture via turbulent mixing, and convertinghydrocarbon fuel into hydrogen rich gas by autothermal reaction using acatalyst.
 19. A method according to claim 14, wherein the reformerreactor further comprises an inner wall and an outer wall forming aspace in-between, wherein the space defines an oxidizing agent passagebetween an oxidizing agent supply port provided in the outer wall and anoxidizing agent inlet provided in the inner wall, and wherein preheatingof the oxidizing agent is performed by heat exchange from the inner wallto the oxidizing agent.
 20. A method according to claim 14, whereinpreheating the hydrocarbon fuel is performed by a fuel preheating meanswhich is an integral part of the fuel inlet.
 21. A method according toclaim 14, wherein preheating of the hydrocarbon fuel is performed byheat exchange from the one of the two side faces to the fuel inlet. 22.A method according. to claim 14, wherein the hydrocarbon fuel is sprayedinto the reaction chamber by a fuel injector.
 23. A method according toclaim 14, comprising using a reformer reactor for converting hydrocarbonfuels into a hydrogen rich gas for fuel cells and/or exhaust treatmentapplications by auto-thermal reaction comprising a housing with two sidefaces forming a reaction chamber of the reformer reactor, a fuel inletwhich is provided in one of the two side faces for providing hydrocarbonfuels into the reaction chamber, wherein hydrocarbon fuel and oxidizingagent are brought together in the reaction chamber, an inner wall and anouter wall forming a space in-between, wherein the space is defines anoxidizing agent passage between an oxidizing agent supply port providedin the outer wall and an oxidizing agent inlet provided in the innerwall, a fuel preheating means which preheats the hydrocarbon fuel beforethe hydrocarbon fuel enters the reaction chamber, the preheating meansbeing an integral part of the fuel inlet, the inner wall being adaptedto preheat the oxidizing agent to substantially the same or to a highertemperature range as the hydrocarbon fuel.